Magnetic media are important information storage devices, prominent examples of which are hard disk drives and magnetic memory devices such as MRAM. Magnetic media are generally characterized by a surface with an addressable pattern of magnetic properties that enable localized alteration of a detectable property of the surface. Typically, domains of magnetically active material are separated by domains of magnetically inactive material, so that a magnetic property of one domain, such as residual magnetism, can be made different from that of a neighboring domain.
Storage densities of magnetic media rise inexorably with time. As storage densities rise, the size of the addressable domains is reduced, and the separating domains grow smaller. Such trends create challenges in maintaining separation and addressability of the domains. For example, as magnetic domains grow smaller and closer together, maintaining a detectable separation of the magnetic fields present in the domains becomes more difficult. As storage densities have passed the 1 Tb/in2 mark, bit patterning of magnetic surfaces has emerged as a promising path to further densification, but with domain sizes smaller than 50 nm, standard patterning techniques such as lithography are exhausted.
Nanoimprint patterning is currently used to create features smaller than 50 nm on magnetically active surfaces. A film of a curable mask material, typically an amorphous carbon material, is applied to a substrate having a magnetically active surface. The film is physically imprinted with a pattern and then cured to form a patterned mask that may have features smaller than 10 nm. Such a patterned mask forms the basis for a patterning operation resulting in a pattern of magnetic properties in the magnetically active surface.
A hardmask is frequently applied between the magnetically active surface and the patterned mask. The hardmask is patterned by etching through the patterned mask, and provides a more robust mask material for the subsequent processes that produce the magnetic pattern on the substrate. In many cases, the processes used to alter the magnetic properties of the substrate involve plasma implantation, which may degrade soft masking materials, altering the pattern formed therein. The hardmask provides better resistance to the plasma environment than does the patterned mask described above.
The hardmask is not perfect, however. For very small features, degradation observed in amorphous carbon hardmasks during, for example, plasma implantation patterning processes in enough to render the magnetic properties of the small domains indistinguishable. Thus, there is a continuing need for better patterning materials, processes, and apparatus for patterning of magnetic media.